In more traditional four cycle engines using conventional distributors, the cylinder identification was easy to accomplish since each spark plug fired only once per complete engine cycle. Thus, off-board engine diagnostics equipment would only need a single lead sensing the firing of the number one cylinder in order to determine the engine rotational position. In the current distributorless wasted spark systems, however, the spark plug in a cylinder will fire twice per complete engine cycle, which corresponds to two crankshaft rotations per cycle. Therefore, the existing off-board diagnostics equipment could not distinguish in which half of the engine cycle the spark was firing for a particular cylinder. The plug firings that occur during the half of the engine cycle producing combustion are termed the power stroke, while those occurring on the exhaust stroke are termed wasted stroke. The terms power stroke and wasted stroke used herein are merely a convenient way to distinguish the combustion half of the engine cycle, comprising the compression stroke and power stroke, from the exhaust half of the engine cycle, comprising the exhaust stroke and intake stroke.
The most direct way to solve this ambiguity, is to mount a sensor to the engine which can determine the rotational position of a camshaft, thus determining which half of the engine cycle the engine is in at all times. Currently, nevertheless, many distributorless ignition systems using the wasted spark method, do not employ a camshaft driven sensor to determine the exact rotational position of the engine. While this is sufficient for conventional engine operation, it does not provide sufficient information for engine diagnostics or more advanced engine operation, such as sequential fuel injection systems. Accordingly, for the purpose of engine analysis and diagnostics for wasted spark systems without CID sensors, an off-board apparatus is needed that can determine which half of the cycle the engine is in. And furthermore, an on-board apparatus is needed that could be inexpensively built into the engine system, thereby eliminating the need for an additional expensive camshaft driven sensor.
More recently, off-board engine diagnostics equipment has been developed with the ability to determine when a cylinder firing event is associated with the beginning of a power stroke rather than a wasted spark firing. Most notably, systems have been developed which can separately measure the voltage drops and calculate the difference in magnitudes of voltage drops, called the breakdown voltage, across pairs of spark plugs connected to opposite ends of the same coil. These corresponding spark plugs are disposed in cylinders which are one half phase apart, i.e., 360.degree. out of phase with one another. This measurement is useful because the voltage drop is larger on the cylinder entering its power stroke than it is on the corresponding cylinder which experiences a wasted spark firing. Up until now, this has been accomplished by using multiple sensors connected to the ignition cables, running between the spark plugs and coils, which transmits the data to a microprocessor that must sort and process these signals. This requires significant computing power in that each cylinder produces signals that are sent to the microprocessor, and these individual signals are then added together electronically to determine which of the two firing events produce a greater voltage drop, before further processing of this information can be done to determine which cylinder was entering its power stroke. Additionally, this type of system takes significant time to hook up since several sensors must be installed.
Also, more recently, some engines require on-board capability of determining the cylinder identification, particularly those using sequential fuel injection. This is currently accomplished using a camshaft driven sensor which directly detects the rotation of a camshaft. These sensors can be quite expensive to add to the current engine systems.